Adding TimeZone to system

There are some additional time zones added such as:

1.GMT 13:00 Tonga Standard Time (Tongatapu)

2.GMT United Kingdom Time (London)

3.GMT 05:30 India Standard Time (Kolkata)

For instance when i use "Asia/Kolkata" instead of "GMT 05:30 India Standard Time (Kolkata)", it works fine. But when i use the later, all times are taken according to system time.In short it is not recognizing the time zones as correct.

Please help me understand where in back end it is coded to recognize the values OR how can we make use of added time zones.